High Zircon Fire Brick for Glass Furnace Bulk Density ≥5g/cm3 MgO Content 0.01-0.12%

Refractory High-pure zircon bricks

Pure zircon brick is a zircon-based crystal phase, referred to as high zirconium brick, and is one of the important types of zirconium-containing refractories.

1. Production of pure zircon bricks

(1) Raw material processing.

The raw material of the zircon brick is a selected zircon ore, referred to as zircon sand. The mass fraction containing zircon is about 90%.

The zircon concentrate sand has a fine particle size and is single, generally 0.1-0.2 mm. It is not suitable to directly make refractory bricks. In order to obtain pure zircon refractory bricks with coarse particles, it is usually pre-calcined or high-temperature melted to form zircon clinker agglomerates. When calcining the clinker, a part of the concentrate sand is first ground into a fine powder, mixed with another part of the concentrate sand, and bonded with a temporary organic binder to form a ball or a blank, at 1500-1700 degrees (lower than the zircon decomposition temperature). Calcined into dense agglomerates. If an alkali metal oxide or a mineralizer such as MgO or GaO is present, it can be calcined at a lower temperature of 1050 degrees or more. Zircon sands shrink from 900 degrees when calcined, tends to shrink when it reaches about 1350 degrees, and then expands, and then shrinks sharply after 1700 degrees. The zircon concentrate sand mass is improved in compactness after calcination, and the bulk density can reach 3.5g/cm3 or more.

If pure zircon products are produced from fine powder, the concentrate sand can be directly calcined at 1450 degrees, loosened by quenching, and then ground.

(2) Production of high zirconium bricks.

For the production of pure zircon products, temporary binders such as sulfite pulp waste liquid, dextrin and lignin may be used, and ethyl silicate, calcium alkylate and phosphoric acid, and water glass may also be used. If a plastic refractory clay is used as a binder, the product is easy to form and sinter, but it tends to cause a decrease in the refractoriness and volume stability of the product. Especially when the amount of clay added to the ingredients is high, the effect is particularly significant.

In order to promote the sintering of pure zircon products, a small amount of CaO, Ca(OH)2, MgO or MgF2 and other mineralizers are often added to the ingredients. This additive promotes the decomposition of ZrO2•SiO2 at high temperatures, forms a ZrO2 solid solution with ZrO2 and enters the glass phase, thereby promoting sintering.

When it is formulated with pure zircon, in order to ensure the good properties and precise shape of the product, the particle size, the amount of the binder and the amount of the admixture must be precisely matched. For articles containing coarse particles of all levels. Multi-stage particle batching is required, and the specific surface area and amount of the fine powder should be higher than that of the ordinary refractory brick to facilitate the formation of a dense green body and to facilitate sintering. If the body consists entirely of fine particles, the maximum particle size of the fine powder is usually below 44 microns, with a few micrometers being the majority. When molding, according to the requirements of the bulk density of the product, ordinary products are generally formed by the method of squeezing mud and dry pressing; the dense ones are mostly cast by mud; the high-density is commonly used for mud casting and isostatic pressing. The various components in the furnish should correspond to the forming method. Pure zircon products must be fired at higher temperatures, and higher density products require higher temperatures. According to the nature and content of the fine powder in the green body and the type and quantity of the mineralizer, the highest firing temperature is generally about 1700 degrees, which should be controlled at a temperature at which the sintered surface of the green body does not undergo significant deformation, and is in contact with the holding time. correspond.

Refractory High-pure zircon bricks Physical and chemical index

Properties and applications of high zirconium bricks
(1) Properties of high zirconium bricks.

The pure zircon product contains ZrO2 with a mass fraction of about 65%, almost entirely composed of zircon crystals, and only a very small amount of glass phase and free ZrO2. The true density is about 4.55g/cm3, the highest is 4.62g/cm3, the bulk density of common products is 3.6-3.8g/cm3, the apparent porosity is more than 13%; the dense refractory brick has a bulk density of 3.8-4.0g/cm3; the apparent porosity is 5%. Left and right; high-density product, bulk density greater than 4g/cm3, apparent porosity is less than 1.0%.
Since the product is almost entirely composed of zircon crystals, it contains only a very small amount of glass phase, and the viscosity is also high at high temperatures, so the refractoriness is high, greater than 1825 degrees. The normal temperature compressive strength of the product is 100-430 MPa, and the flexural strength is 17.8-76.3 MPa. The load softening temperature is greater than 1650 degrees, and increases with the decrease of mineralizer and the increase of firing temperature, and the highest can reach 1750 degrees. Therefore, it is a refractory brick which is excellent in resistance to heat and heavy load at high temperature and has good wear resistance.
Zircon has a low thermal expansion and is fired at a high temperature, so that the volume stability of the product is high. The room temperature to 1400 ° C, the coefficient of thermal expansion is only 0.5%. Reburning at 1500 degrees for 2 hours, the residual shrinkage rate is only 0.04%~0.20%. Some products were re-fired at 1650 ° C without any residual shrinkage.
The high-density zircon product has poor thermal shock resistance when there are no coarse particles therein. It must be heated or cooled slowly during use. When the product is composed of multi-stage particles, the thermal shock resistance is remarkably improved.
Such articles are not susceptible to wetting and erosion by molten metal and slag, and are particularly resistant to wetting by aluminum and its alloys. Therefore, it has good resistance to slag, metal liquid and glass liquid erosion. Highly dense products perform better, for example, by alkaline slag, which is only about 1/3 of that of mullite.

(2) Application of high zirconium bricks.
Zircon products can be used as linings in steel drums for continuous casting and other parts that are extremely eroded by slag. They can also be used as casting ports for copper and aluminum smelting furnaces. It can also be used in places where the glass melting furnace is in direct contact with the glass liquid and the upper structure, and as an insulating brick between the fused zirconium corundum brick and the silicon brick.

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